Unit 7 - Atomic, Nuclear and Particle Physics
In this unit, physics had the idea to incorporate Pokemon into this unit. You'll see what i mean later. 7-1 The Atom One day, Ernest Rutherford decided to shoot some alpha particles at a thin piece of gold foil. He found that most of the particles went right through it, while some of it bounces off slightly to the sides and even less bounced in large angles. He declared his victory by saying that: * Atoms are mostly empty * Atoms have a very small and very hard positively charge thing in the middle that we call the nucleus. Then Bohr Rutherford came in and said: I WANT TO MAKE A DIAGRAM FOR THIS SHIZ So his rules for his diagram is: * Electrons can only exist in particular orbits around the atom * Electrons radiate energy in forms of waves when they drop energy levels from allowable orbits. ** Explains why atoms only absorb/emit specific wavelengths of light * He did not explain why only these particular orbits/energy levels were allowed Louis deBroglie decided to add on to Bohr's stuff: * Light can be both wave and particles * Electrons can be also thought of as acting like waves * Electrons only have certain discretes (distinct) amounts of energy, multiples of the wavelength of an electron. This explains the orbits. * Orbits described, are not actually orbits, but instead 3-D energy waves Formula λ = hc/E λ = Wavelength h = 6.63 x 10-34 (Planck Constant) c = 3 x 108 E = Energy 7-2 Particle Physics For every existing particle, there is an "anti-particle" and it has the same properties except an opposite charge. If they go touchy touchy on the same kind of the anti-particle, they destroy each other. The symbol for anti-particles are same for its normal particle, except with a line on the top. Scientists were like: hey look! We should make this more complicated by implementing quarks into the system! Essentially, matter are made of quarks These are the six names of quarks A Hadron is a particle made up of quarks. * Baryons are made of 3 quarks ** Protons have 1 down + 2 up quarks (2/3 + 2/3 - 1/3 = charge of 1) ** Neutrons have 2 down + 1 up quark (2/3 - 1/3 - 1/3 = charge of 0) * Mesons are made of 2 quarks. These are very unstable. Each quark also has an anti-quark, again same properties but opposite charge. Thus 1 anti-up + 1 down = charge of -1. Leptons are particles in the electron family, having a charge of -1. This consists of the electron (e-), the mu (u-), and the tau (T-). There are also neutrinos associated with each of the leptons (Ve, Vu, VT). And there are an anti-particle for each of the 6 normal leptons. Thus 12 leptons in total. In addition the the laws of conservation of momentum and mass, a reaction must also conserve: * Total Charge * Baryon Number - If baryon, the number is 1. If not, then it's 0. If it is anti-particle, -1. * Lepton Number - If lepton, the number is 1. If not, then it's 0. If it is anti-particle, -1. * Strangeness - number of strange quarks present. Anti-strange quarks still count positively. The Strong force keeps the quarks together. Let's see some examples: p + n -> p + p * Total Charge is not conserved p + n -> p + p + e- * Lepton number is not conserved n -> p + e- + anti-neutrino * Everything is conserved 7-3 Fundamental Forces Four fundamental forces, from strongest to weakest: # Strong Force (bonds protons and neutrons together) # Electromagnetic (magnets, friction, normal forces) # Weak Force (nuclear decay) # Gravity These forces do not have to be in contact with each other to be felt (e.g. you don't need to touch the ground to feel gravity, but you have to push a box to feel the box's force on you). Bosons are force carriers, and that's how these force works. Feynman Diagrams Follow these steps when drawing them: Incoming particles come up from bottom * Outgoing particles leave through the top * Boson that carries out this reaction shown in the middle. Here are links to help you draw that: http://teachers.web.cern.ch/teachers/archiv/HST2002/feynman/examples.htm http://www.xplora.org/downloads/Knoppix/CERN/Feynman.pdf http://www.quantumdiaries.org/2010/02/14/lets-draw-feynman-diagams/ https://www.youtube.com/watch?v=qpQJ_ud5Xuo http://www.learner.org/courses/physics/unit/intro.html http://www.quantumdiaries.org/2010/02/14/lets-draw-feynman-diagams/ https://www.youtube.com/watch?v=hk1cOffTgdk http://www-pnp.physics.ox.ac.uk/~barra/teaching/feynman.pdf 7-4 Radioactivity Definitions Proton/Atomic Number: # of protons in an atom Neutron Number: # of neutrons in an atom Nucleons: Protons and neutrons in the atom Nucleon Number (mass number): Proton # + neutron # Nuclide: Atom with specified # of protons and neutrons Isotopes: nuclei with same # of protons, different # of neutrons Radioactivity A stable atom has a balance between two fundamental nuclear forces: * The Electromagnetic force between protons, which tries to break apart the nucleus (because protons want to push each other away) * The Strong nuclear force caused by neutrons, which tries to keep nucleus together. If these forces are not balanced, then the atom becomes unstable and will tend to decay. * In smaller atoms, they must have the same number of protons and neutrons to be stable. * In larger atoms, they must have more neutrons to hold the atom together. * Atoms with too many neutrons will tend to undergo B- Decay * Atoms with too little neutrons will tend to undergo B+ Decay * We will focus on Alpha, Beta -, and Gamma decay Alpha Decay: Two protons and two neutrons are lost Beta Decay: One of the neutrons turns into a proton and an electron. Mass number remains the same, atomic number increases by 1. The product must have a neutrino Gamma Decay: Nothing is lost or gain. Energy is simply released as EM waves Biological effects * Radioactive particles can damage enzymes and structure molecules that are vital to the workings of a cell. * This can directly damage cells (such as radiation burns) or systemic damage (radiation sickness) * Alpha particles will damage more cells as it spreads over a larger area * Beta particles will damage less, but penetrate deeper. Exponential Decay and Half life In a sample of atoms, they will decay randomly, so one day scientists decided to play Half-Life, and was so obsessed with it that they called this way of measuring decay "Half-life". Half-life is now a common way of measuring the ray of decay of a sample. It is defined as "the time after which half the radioactive particles will have undergone radioactive decay." The radioactive same can be measured in three ways: * The mass of unreacted atoms * The number of unreacted atoms * Activity of the sample (used for isotopes with low half-lives) E.g. A sample that contains 2000 radioactive nuclei has a half life of 3 days. How long till there are 250 particles left? Answer: 9 days because after first 3 days 2000 -> 1000. After 3 more days 1000 -> 500. After 3 more days 500 -> 250. 7-5 Binding Energy We like to use amu for unified atomic mass unit. 1u = 1/12 of the mass of carbon-12 atom. We use the eV (electron-volt), and 1 eV = 1.6 x 10-19J Neutrons and Protons that are alone generally have larger masses than if they are contained inside of a nucleus. In another words, if the nucleus was broken up, it would have more mass in total. The energy required to break it apart is calculated using the famous formula: E=mc2 (m in kg, and c is speed of light) How much energy is within a 1g paperclip? E = (0.001kg)(3x108)(3x108) = 9x1013 How about that in MeV? 9x1013 x 931.5 = (some number here I'm too lazy to punch in) Nickel-62 is the most stable atom. Atoms undergo fission, splitting into two or more atoms. Smaller nuclei will tend to undergo fusion, combining two atoms to become larger ones.